1. Field of the Invention
The present invention relates to a motor-assisted drive unit for a motor-assisted vehicle, and particularly to a motor-assisted drive unit for a motor-assisted vehicle in which an assist unit is small-sized.
2. Background Art
A conventional bicycle has been proposed that detects a manual drive torque, or leg-power, and biases a power assist source (DC motor) connected to a drive system in accordance with the detected leg-power in order to assist the leg-power. One example of a drive unit including such a power assist source is disclosed in Japanese Patent Laid-open No. Hei 11-5584. The drive unit is disposed at the back of a crank shaft and its area, wherein a controller casing for housing a controller including electronic parts (power transistor, CPU, and the like) for driving the motor, and a the controller casing projects downwardly from a motor casing for housing the motor.
The conventional drive unit, which includes the controller casing projecting downwardly from the motor casing, is undesirably large.
There is therefore a need for a drive unit to provide a motor-assisted drive unit for a motor-assisted vehicle which is small in size.
To achieve the above object and other objects, according to a first feature of the present invention, there is provided a motor-assisted drive unit for a motor-assisted vehicle, including a motor as a power assist source housed in a casing, including a control board on which control devices of the motor are mounted; wherein the control board is provided in the casing so as to be disposed in a direction substantially perpendicular to the motor shaft of the motor; and at least part of the control board extends, as seen along the axial direction of the motor, to a position at which it is overlapped with the motor.
With the above feature, since part of the control board is overlapped with the motor, as seen along the axial direction of the motor, the motor-assisted drive unit can be made as small in size as possible, and since the area of the control board extends to a position at which it is overlapped with the motor, the inner space of the casing can be efficiently used.
According to a second feature of the present invention, a CPU as one of the control devices of the motor is mounted on a portion, overlapped with the motor, of the control board, so as to project in a gap between the overlapped portion of the control board and the motor. According to this feature, it is possible to dispose a CPU having a relatively large mounting area in the conventional dead space.
According to a third feature of the present invention, there is provided a motor-assisted drive unit for a motor-assisted vehicle, including a motor as a power assist source housed in a casing, including a first control board and a second control board on each of which control devices of the motor are mounted; wherein the first and second control boards are disposed in the casing so as to extend in the direction nearly perpendicular to the motor shaft of the motor; and the second control board is overlapped, as seen along the axial direction of the motor, to part of the first control board.
According to the third feature, since the second control board is overlapped with part of the first control board, as seen from the axial direction of the motor, the motor-assisted drive unit can be made small in size. Further, control devices mounted on the first and second control boards can be efficiently disposed in consideration of the correlation between the control devices, and the first and second control boards can be disposed in the casing without occurrence of a dead space.
According to a fourth feature of the present invention, control devices, typically, a CPU, a capacitor, and a relay are mounted on the first control board, and a FET is mounted on the second control board. With this feature, the control devices having relatively small heat generation, such as the CPU, capacitor, and relay, are mounted on the first control board separate from the FET on the second control board, which has a relatively large heat generation. It is therefore possible to prevent the heat generated from the FET from being directly transferred to the control devices such as the CPU, capacitor, and relay.
According to a fifth feature of the present invention, the first control board is configured as a printed wiring board, and the second control board is configured as a light metal board. Also, according to a sixth feature of the present invention, the second control board is directly attached to the inner wall surface of the casing, and the first control board is disposed over the second control board with a gap disposed therebetween. According to these features, it is possible to easily transfer the heat, which is generated from the FET and the like mounted on the second control board, to the casing via the light metal board, and to minimize heat from affecting the first control board.
According to a seventh feature of the present invention, the control board is elastically supported on the casing; according to an eighth feature of the present invention, the control board is elastically supported by using a vibration-proof rubber disposed around a casing boss portion for rotatably supporting the motor shaft of the motor; and according to a ninth feature of the present invention, the vibration-proof rubber is compressed between the control board and a motor supporting portion of the casing. With these features, transmission of vibration to the control board is retarded, which stabilizes the operation of the electric parts mounted on the control board, thereby prolonging the service life of the electric parts.
According to a tenth feature of the present invention, the control devices of the motor are mounted on both surfaces of the control board; a semiconductor device and a board having a good thermal conductivity at least part of which is in contact with the semiconductor device are provided on the surface, on the casing side, of the control board; and the board having a good thermal conductivity is in contact with the casing. With this configuration, it is possible to effectively transfer heat generated from the semiconductor device by a simple, inexpensive structure.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.